The main motivation for this change is to make sure that higher-level
code deals with the fact that self.units.number can be None, and has
an easy way to do so.
I'm not sure all our code is *currently* doing the right thing for this
case, because I'm not sure it will ever actually come up. It's possible
that earlier Beancount plugins fill in decimal amounts for postings
that are originally loaded with self.units.number=None. I'll have to see
later whether this case comes up in reality, and then deal with it if so.
For now the safest strategy seems to be that most code should operate
when self.units.number is None.
Mostly this meant giving annotations to low-value functions like
the error classes and __init_subclass__, but it's worth it for
the future strictness+documentation value.
Our version of Posting is interface-compatible with Beancount's,
but makes stronger guarantees about the data types for our
higher-level code to rely on.
* Rename _typing to beancount_types to better reflect what it is.
* LessComparable isn't a Beancount type, so move that to
plugin.core with its dependent helper classes.
* Errors are a core Beancount concept, so move that module to the
top level and have it include appropriate type definitions.
I feel like posting hooks a case of premature optimization in early
development. This approach reduces the number of special cases in
the code and allows us to more strongly reason about hooks in the
type system.
This is the layer that keeps track of the different groups of hooks and
can filter them before runtime. The idea here is that you'll be able
to do things like skip hooks that require network access when you don't
have it, or skip CPU-intensive hooks when you don't need them, etc.
Python's own enum works fine for the simple values that expenseAllocation
uses, but it won't work as well for metadata like taxImplication where
many of the values aren't legal Python identifiers. Introduce our own
MetadataEnum class with the necessary functionality, and switch to that.
This is the simplest version of a common validation we're going to do:
make sure that a particular piece of metadata has one of a set of
values.
This checker needs some bounds checking but I wanted to err on the
side of committing this early because it introduces so much base
infrastructure.
